Rats exposed during gestation and through 30 to 60 days postpartum to halothane have been shown to exhibit certain behavioral deficits when tested at 75 to 150 days of age, and to have a dose-dependent loss of up to 24% of synapses in the sensorimotor cortex at that age. The present studies propose to study rats dosed either continuously or intermittently at 100 ppm halothane in air for further analysis of these effects in the sensorimotor cerebral cortex and hippocampus of the rat. The effect of halothane on synaptogenesis will be investigated by an analysis of dendritic growth and spines as revealed by the rapid Golgi stain, under the computerized scanning light microscopy. Dendritic growth analysis will be extended by electron microscopic observation of dendritic and axonal growth cones with special emphasis on microfilaments, filopodia, and synapses. In addition, behavioral effects assessed by visual discrimination and maze tests, will be analyzed with respect to the hypothesis that the effects of halothane on adult behavior is mediated via suppression of synaptogenesis, and may be dominated by distrubance of hippocampal development. The animal model proposed will provide information essential for understanding the functional mechanism of neurotoxicity and help establish an adequate safety measure for operating room personnel. This study also offers the possibility that halothaneexposure can be developed into a research tool of analytical use, in which the main action desired is the suppression of synaptogenesis.